It is known that the air beneath an aircraft wing tends to move around the wingtip from the bottom, which has a greater air pressure, to the top, which has a lower air pressure, thereby creating vortices which contribute to the inefficiencies of the wing and reduce its lifting power. In other words, under lifting conditions, an airfoil creates a vortex system which is shed along its span, with a concentrated vortex centered just behind each wingtip. This vortex system is a by-product of lift which is not necessary for the production of lift and is a major source of aircraft induced drag. The vortex or rotational air flow developed at or near the wingtip of an aircraft induces a rolling moment which comprises both rotational and axial components of the vorted velocity of the vortex.
Various attempts have been made to limit the vortex effect to decreaase both induced drag and danger to following aircraft. For instance, U.S. Pat. No. 2,485,218 to Shaw, dated Oct. 18, 1943, shows an airfoil rotor forming the actual wingtip itself, the rotor being powered either by a motor or a propeller located in front of the wingtip. The rotor is rotated in a direction to cause circulation opposing the normal wingtip vortex, thereby influencing the airflow around the tip of the aircraft wing to reduce the induced drag of the vortex.
Similar approaches are shown in U.S. Pat. Nos. 3,984,070 and 4,533,101 to Patterson, Jr., dated Oct. 5, 1976 and Aug. 6, 1985, respectively. Both of these patents show blades or propellers behind the aircraft wingtips to force a breakup of the rotational air flow of the vortices. In the earlier patent, the blades are not powered. In the latter patent, the blades are power rotated opposite the direction of the vortex to attenuate or mitigate the vortex effects. In all of these approaches, efforts are made to breakup both the rotational and axial components of the vorted velocities and in no way are directed to generating power from the vortices.
U.S. Pat. No. 4,045,144 to Loth, dated Aug. 30, 1977, shows a grounded wing energy concentrator which employs a turbine disposed outside the rolled-up vortex. Duct means provide fluidic communication between the turbine and the rolled-up vortex to extract power therefrom, and an air inlet is provided for the turbine. However, although the Loth concentrators extract energy from the ground wind induced vortices, the turbines include blades which react against the axial or longitudinal component of the vorted velocity of the vortex. If such a concentrator were used in an aircraft, even though energy would be extracted from the vortex by the turbine and, thereby, reduce the aircraft drag, some component of drag would be added back into the system because the turbine blades oppose the axial component of the vorted velocity of the vortex.
This invention is directed to a new and improved apparatus for generating power from a wingtip induced vortex without, itself, creating any drag on the system. The power derived from the apparatus is used to drive various systems of the aircraft.